In recent years, 3GPP (3rd Generation Partnership Project) is under consideration of introducing LTE (Long Term Evolution) as a next generation mobile communication system and the standardization thereof is in progress (see NPTL 1, for example).
As shown in FIG. 15, in LTE, an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) is formed by using a plurality of radio base stations (eNB: enhanced Node B) 10_1 to 10—i. A user equipment (UE) 20 attaches to one of cells formed by the eNBs 10_1 to 10—i to perform desired communication. Moreover, each of the eNBs 10_1 to 10—i is connected to an MME (Mobility Management Entity) 30. The MME 30 has functions corresponding to a core network in the existing mobile communication system and performs various control on the eNBs 10_1 to 10—i. Note that in the following explanation, the eNBs 10_1 to 10—i may be collectively referred to by a numeral 10.
An interface between the eNB and the MME is defined as an S1 interface, an interface between the eNBs is defined as an X2 interface, and a wireless interface between the eNB and the UE is defined as a Uu interface, respectively.
Further, introduction of the LCS is also taken into consideration for the standardization by 3GPP (see NPTL 2 to 4, for example). Typically, in the LCS, a geographical location of the UE is detected, and a service intended for a subscriber corresponding to the location and the like are provided.
Specifically, as shown in FIG. 16, a mobile communication system realizing the LCS includes the above eNB 10, UE 20, MME 30, and an E-SMLC (Evolved Serving Mobile Location Centre) 40 which is a service provider. An interface between the E-SMLC and the MME is defined as an SLs interface.
The function of the E-UTRAN in the LCS is to acquire information regarding a reception status at the UE of a radio signal (RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality) etc.) in order to calculate the geographical location and direction, and to notify the E-SMLC of the acquired information. This function is referred to as a UE Positioning function.
One of the UE Positioning functions is an Uplink E-CID (Enhanced Cell ID) Positioning Procedure.
Hereinafter, an operation of the mobile communication system regarding this procedure will be described in detail with reference to FIGS. 17, 18, 19A to 19C, and 20.
As shown in FIG. 17, the eNB 10 firstly receives, from the E-SMLC 40 through the MME 30, an E-CID MEASUREMENT INITIATION REQUEST which is a kind of LLPa (LTE Positioning Protocol Annex) messages (step S101). Note that the LLPa message may be referred to as “LLPa:XXX (arbitrary message type)” in the following explanation upon mentioning the LLPa message.
The E-CID MEASUREMENT INITIATION REQUEST message is typically a request to acquire necessary information for calculating the geographical location and direction. In the example shown in FIG. 17, both RSRP and RSRQ are requested as the necessary information (however, either RSRP or RSRQ may be requested as well). Moreover, “On Demand” indicating only one notification of the necessary information or “Periodic” indicating periodic notification of the necessary information is also designated in the E-CID MEASUREMENT INITIATION REQUEST message.
Then, the eNB 10 transmits to the UE 20 RRCConnectionReconfiguration which is a kind of RRC (Radio Resource Control) messages, thereby instructing the UE 20 to report the necessary information (step S102). Note that the RRC message may be referred to as “RRC:YYY (arbitrary message type)” in the following explanation upon mentioning the RRC message.
Measurement Object, Reporting Configuration, Measurement Identity, s-Measure, Measurement Gap (MeasGap) and the like are set to the RRCConnectionReconfiguration message.
Among them, the Measurement Object includes information concerning a frequency which the UE 20 should measure and a neighbouring cell (a cell formed by another radio base station disposed adjacent to the eNB 10).
FIG. 18 shows some arrangement examples of neighbouring cells. Among them, an Intra-Freq neighbouring cell 51 operates in the same frequency as a serving cell (a cell formed by the eNB 10) 50 and a part of coverage of the intra-Freq neighbouring cell 51 overlaps coverage of the serving cell 50. Both Inter-Freq neighbouring cells 52A and 52B (hereinafter may be collectively referred to by a numeral 52) operate in a difference frequency from the serving cell 50. Meanwhile, coverage of the cell 52A includes the coverage of the serving cell 50 (substantially equivalent to the coverage of the serving cell 50 or larger than the coverage of the serving cell 50). On the other hand, a part of coverage of the cell 52B overlaps the coverage of the serving cell 50. Further, both Inter-RAT neighbouring cells 53A and 53B (hereinafter may be collectively referred to by a numeral 53) are formed by radio base stations to which Radio Access Technology (RAT) different from the eNB 10 is applied. Meanwhile, coverage of the cell 53A includes the coverage of the serving cell 50. On the other hand, a part of coverage of the cell 53B overlaps the coverage of the serving cell 50. All of these neighbouring cells 51 to 53 could be designated objects to be measured by the UE 20.
Next, in the Reporting Configuration, an event type for the UE 20 to use in a report of a measurement result and reporting condition thereof are designated. Additionally, the abovementioned “On Demand” or “Periodic” is also designated in the Reporting Configuration.
Next, the Measurement Identity is composed of measId, measObjectId, and reportConfigId. The measObjectId is defined in one-to-one association with the above Measurement Object. That is, the UE 20 can comprehend the information concerning the frequency to be measured and the information concerning the neighbouring cell from the measObjectId. Moreover, the reportConfigId is defined in one-to-one association with the abovementioned Reporting Configuration. That is, the UE 20 can comprehend the event type to be used in the report of the measurement result and the reporting condition thereof from the reportConfigId. Further, the measId is an identifier for associating the measObjectId with the reportConfigId. In the example shown in FIG. 17, the eNB includes in the RRCConnectionReconfiguration message certain measObjectId#2 and reportConfigId#2, and measId#2 for associating them.
Next, to the s-Measure, a threshold is set as a measurement condition for the neighbouring cell with the matching measId. The UE 20 compares this threshold with RSRP of the serving cell, and performs measurement of the neighbouring cell when the RSRP of the serving cell is less than or equal to the threshold. That is, when the RSRP of the serving cell is less than or equal to the threshold, the UE 20 performs measurement of both the serving cell and the neighbouring cell. On the contrary, when RSRP of the serving cell exceeds the threshold, the UE 20 performs measurement of only the serving cell and not the neighbouring cell. Moreover, as shown in FIG. 17, when the threshold is not set to the s-Measure, the UE 20 immediately measures both the serving cell and the neighbouring cell.
A benefit of not setting the threshold to the s-Measure typically lies in the point that the E-SMLC 40 can calculate the geographical location and direction of the UE 20 with high accuracy.
Specifically, in a case where the threshold is set to the s-Measure and the RSRP of the serving cell exceeds the threshold, the UE 20 reports RSRP and RSRQ of only the serving cell. The RSRP and RSRQ are used by the E-SMLC 40 to estimate the distance between the eNB 10 and the UE 20, and the like. Under an environment providing favorable wireless transmissions between the eNB 10 and the UE 20, the E-SMLC 40 can accurately calculate the geographical location of the UE 20 only from the RSRP and RSRQ of the serving cell.
However, under an environment with poor wireless transmissions (an environment where buildings are built up, for example), even when the RSRP of the serving cell exceeds the threshold, the E-SMLC 40 may not be able to accurately calculate the geographical location of the UE 20 only from the RSRP and RSRQ of the serving cell.
For example, when RSRP and RSRQ of any one of the neighbouring cells 51 to 53 shown in FIG. 18 are acquired, the E-SMLC 40 can calculate the geographical location of the UE 20 more accurately. In particular, each of the Inter-Freq neighbouring cell 52A and the Inter-RAT neighbouring cell 53A has substantially equivalent coverage to that of the serving cell 50, thus RSRP and RSRQ of these neighbouring cells 52A and 53A are useful for calculation in the E-SMLC 40.
Therefore, the eNB 10 is assumed to transmit to the UE 20 the RRCConnectionReconfiguration message without setting the threshold to the e-Measure.
Lastly, in the MeasGap, a measurement timing (subframe, to be specific) is designated in a case of measuring the Inter-Freq neighbouring cell or the Inter-RAT neighbouring cell.
Then, the UE 20 updates its own configuration in accordance with contents of the received RRCConnectionReconfiguration message (step S103). Assume that configuration information as shown in FIG. 19A is stored to a memory in the UE 20 before the above step S102. In FIG. 19A, s-Measure (50) indicates that the above threshold is set to “50 dB”. Moreover, MeasGap (Release) indicates that the above measurement timing is not set. In this case, as shown in FIG. 19B, the UE 20 adds measId#2, measObjectId#2 and reportConfigId#2 to the memory, and updates the e-Measure to “Not-setup” and the MeasGap to “Setup”.
After that, the UE 20 transmits to the eNB 10 an RRC:RRCConnectionReconfigurationComplete message (step S104).
Moreover, the UE 20 starts measurement of both the serving cell and the neighbouring cell in accordance with the configuration information updated at the above step S103. Then, the UE 20 sets the measurement result to an RRC:MeasurementReport message to be reported to the eNB 10 (step S105_1). Note that when the measurement of the neighbouring cell is not started (in other words, in a case where the threshold is set to the s-Measure and RSRP of the serving cell is less than or equal to the threshold), the UE 20 sets the measurement result of only the serving cell to the MeasurementReport message.
Subsequently, the eNB 10 sets the measurement result reported from the UE 20 to an LPPa:E-CID MEASUREMENT INITIATION RESPONSE message, and notifies it to the E-SMLC 40 through the MME 30 (step S106_1).
In addition, if the abovementioned “Periodic” is designated, the UE 20 repeats measurement in a predetermined cycle, and sets measurement results to MeasurementReport messages to be sequentially reported to the eNB 10 (steps S105_2 to S105—j).
On the other hand, the eNB 10 sets the measurement results from the UE 20 to LPPa:E-CID MEASUREMENT REPORT messages and sequentially notifies them to the E-SMLC 40 through the MME 30 until the eNB 10 receives, at the step S107 described later, an LPPa:E-CID MEASUREMENT TERMINATION COMMAND message from the E-SMLC 40 (steps S106_2 to S106—j).
Then, the eNB 10 stops notifying the E-SMLC 40 of the E-CID MEASUREMENT REPORT message triggered by the reception of the E-CID MEASUREMENT TERMINATION COMMAND message (step S107).
After that, as shown in FIG. 20, the eNB 10 transmits again to the UE 20 an RRCConnectionReconfiguration message in order to return the configuration of the UE 20 to the state before update (step S201). Specifically, the eNB 10 sets the measId#2, s-Measure (50) and MeasGap (Release) in the RRCConnectionReconfiguration message.
Subsequently, the UE 20 updates its own configuration in accordance with contents of the received RRCConnectionReconfiguration message (step S202). Note that in the following explanation, returning the configuration information of the UE 20 to the state before update may be referred to as “configuration removal”. Specifically, as shown in FIG. 19C, the UE 20 removes the measId#2 (together with the measObjectId#2 and the reportConfigId#2 that are stored in association with the measId#2) from the memory, and updates the e-Measure to “50 dB” and the MeasGap to “Release”.
Note that if “On Demand” is designated at the above step S101, the eNB 10 does not need to set the measId#2 in the RRCConnectionReconfiguration message at the above step S201. When “On Demand” is designated, the UE 20 autonomously removes the measId#2 from the memory after transmitting the MeasurementReport message at the above step S105_1.
After that, the UE 20 transmits to the eNB 10 an RRC:RRCConnectionReconfigurationComplete message again (step S203). Thus, the UE 20 operates in a similar manner as before starting the Uplink E-CID Positioning Procedure.